At present a binocular stereoscopic display system has been the mainstream as a three-dimensional display system. The principle of this binocular stereoscopic display system is to display different images to the right and left eyes so that one can obtain a three-dimensional aspect. This binocular stereoscopic display system is disadvantageous in that how an object looks like does not change when one moves his head and changes the viewing angle, that is, the binocular stereoscopic display system does not have motion parallax. Moreover, there is an inconsistency in that a focus of the eye, i.e. the accommodation point, is located on a screen on which images are displayed, and this position thereof does not correspond to the position of a three-dimensional object. It is believed that this inconsistency causes visual fatigue when viewing a three-dimensional image.
It is required for a three-dimensional display to provide more natural three-dimensional images. Such display can be realized by simultaneously displaying a large number of images in different horizontal directions. In a multi-view stereoscopic display system a plurality of view points are positioned in the horizontal direction in a space to display different images to the view points. By reducing the distance between view points to be narrower than the distance between both eyes, different images are displayed on the right and left eyes. Further, by increasing the number of view points, an image is switched to a different one when moving one's head, thus motion parallax can be obtained.
Recently, there has been proposed a method in which a large number of directional images, which are orthographic projection images of three-dimensional objects, are prepared for different projection directions without setting view points in a space, and images are displayed simultaneously with nearly parallel rays in corresponding directions (see, for example, “Three-dimensional Display Using Modified Two-dimensionally Aligned Multiple Telecentric Optical Systems”, Yasuhiro Takaki, The Journal of the Institute of Image Information and Television Engineers, Vol. 57. No. 2, Pg. 293 through 300 (2003)). Natural motion parallax is obtained by increasing the number of directional images to be displayed. Particularly, there is a report describing that, if the number of directional images is 64, the eye can be focused on the three-dimensional image and thereby visual fatigue caused when observing the three-dimensional image can be resolved (see, for example, “Accommodation Responses to 3D Images Consisting of Highly-Density Directional Images”, Takeshi Fukutomi, Hisaki Nate, and Yasuhiro Takaki, The Journal of the Institute of Image Information and Television Engineers, Vol. 58. No. 1, Pg. 69 through 74 (2004)).
As described above, in the three-dimensional display it is necessary to display a large number of images in the horizontal direction. The pixels, which comprise a display screen of the three-dimensional display and are disposed horizontally/vertically, need to have a large number of horizontal display directions and to control the light intensity and color of rays displayed in these horizontal directions. Such pixels are called “three-dimensional pixels”.
As a method of constructing a three-dimensional display having a large number of horizontal display directions, there is known a method of combining a lenticular sheet with a two-dimensional display such as a liquid crystal panel. Here, the lenticular sheet is a sheet on which a large number of cylindrical lenses, which are one-dimensional lenses, are aligned in a direction perpendicular to the central axes of the lenses. The cylindrical lenses comprising the lenticular sheet are disposed so that the focal planes of the cylindrical lenses are located on a display screen of the liquid crystal panel. The display screen of the two-dimensional display consists of a number of pixels disposed horizontally/vertically, and three-dimensional pixels are composed of a plurality of pixels disposed in the horizontal direction and a corresponding cylindrical lens. A horizontal distance between the central axis of the cylindrical lens and each pixel determines a horizontal proceeding direction of a ray after the ray passes through the cylindrical lens, the ray being emitted from the pixel. Therefore, the number of horizontal display directions is equal to the number of pixels used horizontally. This construction method has a problem in which when the number of horizontal display directions is increased, the horizontal resolution of the three-dimensional display is extremely reduced and the horizontal resolution and the vertical resolution of a three-dimensional display become unbalanced.
A method which resolves the above problem is proposed (see U.S. Pat. No. 6,064,424). FIG. 1A is a figure showing a construction method of a conventional technology in which a lenticular sheet is disposed with an inclination in a vertical arranging direction of pixels. FIG. 1A shows a construction method to display color images, wherein the pixels in the figure are RGB color subpixels. One three-dimensional pixel is constructed using M×N number of pixels where M number of pixels are arranged in the horizontal direction and N number of pixels are arranged in the vertical direction, whereby M×N number of horizontal display directions are obtained. In this case, if the inclination angle of the lenticular sheet is θ, θ=tan−1(px/Npy) is established, whereby the horizontal distances between all color subpixels and the central axes of cylindrical lenses can be set to values different from one another within the three-dimensional pixel. Here, px is a horizontal pitch of color subpixels and Py is a vertical pitch of the color subpixels.
In the conventional technology shown in FIG. 1A, one three-dimensional pixel consists of seven color subpixels where N=2 and M=7/2 to realize seven horizontal display directions. In this manner, by tilting the lenticular sheets 3, the three-dimensional pixel can be composed of the color subpixels 2 not only in the horizontal directions but also in the vertical directions. Accordingly, it has been reported that the horizontal resolution of the three-dimensional display can be prevented from being reduced and the balance between the horizontal and vertical resolutions can be improved.